1. Technical Field
The present invention relates to a printing apparatus used in a facsimile machine, a copy machine, a printing apparatus for an OA instrument, or the like, to a printing apparatus control program, and to a printing apparatus control method. In particular, the present invention relates to a printing apparatus that is suitable for performing so-called ink jet printing by ejecting fine particles of liquid ink of a plurality of colors on a printing paper (that is, a recording medium) and rendering a predetermined character or image, to a printing program, to a printing method, and to a recording medium having recorded thereon the program.
2. Related Art
Hereinafter, an ink jet printing apparatus (for example, a printer) will be described as an example.
A printer that uses an ink jet system (hereinafter, referred to as an ‘ink jet printer’) is configured such that a moving body called a carriage having an ink cartridge and a printing head integrally formed therein reciprocates on a printing paper in a direction orthogonal to a paper feed direction (a widthwise direction of the printing paper) and ejects (jets) particles of liquid ink in dot shapes from nozzles of the printing head. Then, a predetermined character or image is rendered on the printing paper, and a printed matter desired is created. Further, ink cartridges of four colors (black, yellow, magenta, and cyan) including black and printing heads for the respective colors are provided in the carriage. Therefore, in addition to monochrome printing, full color printing is easily performed by combining the colors (in addition, color printing of six, seven, or eight colors including the above four colors, light cyan, light magenta, and the like is put into practice).
Further, in the ink jet printer that allows the printing head on the carriage to reciprocate in the direction orthogonal to the paper feed direction (that is, the widthwise direction of the printing paper) for printing, it is necessary to cause the printing head to reciprocate several tens times to one hundred times or more for vivid printing of one page. Accordingly, it takes much time for printing compared to other printing apparatuses, for example, a laser printer using an electrophotography technique, such as a copy machine. Meanwhile, such an ink jet printer is generally referred to as ‘multi-pass printer’ or ‘serial printer’.
In the ink jet printer which has a printing head having the same length as a printing paper width and does not use a carriage, single-pass printing can be performed, without moving the printing head in the widthwise direction of the printing paper, such that fast printing can be performed like the laser printer. Further, the carriage on which the printing head is mounted or a driving system for moving the carriage is not required, such that a printer case can be made small and light-weight. In addition, silence can be significantly enhanced. Such an ink jet printer is generally referred to as ‘line head printer’.
However, the printing head that is an essential part for the ink jet printer is configured such that fine nozzles each having a diameter of 10 μm to 70 μm are arranged in serial by predetermined intervals or arranged in a multi-stage manner in a printing direction, and thus ink ejection directions of some nozzles may be inclined or nozzle positions may be deviated from ideal positions due to a manufacturing error. Accordingly, dots to be formed by the nozzles are deviated from target points, which results in so-called ‘flying curve phenomenon’.
As a result, defective printing occurs on a portion corresponding to the defective nozzle, which is called ‘banding (band) phenomenon’, thereby significantly degrading printing quality.
In particular, such a banding phenomenon may more frequently occur in the line head printer, in which the printing head is fixed (single-pass printing) and the number of nozzles is much greater than the number of nozzles of the multi-pass printer, than in the multi-pass printer described above (in the multi-pass printer, there is known a technique for causing the printing head to reciprocate several times so as to make a white band almost unnoticeable).
Accordingly, in order to prevent a kind of defective printing due to the banding phenomenon, the research and development on the hardware configuration, such as the enhancement of a printing head manufacturing technique or design improvement has been made carefully, however, it is not easy to provide a printing head which does not cause ‘banding phenomenon’ at all in view of a manufacture cost, printing quality, a technique, and the like.
As a result, a technique for reducing the banding phenomenon using a so-called software method, such as a printing control described below, is used in combination with the hardware improvement described above at the present time.
For example, in JP-A-2002-19101 or JP-A-2003-136702, in order to cope with a nozzle variation or non-ejected ink, a shading correction technique is used for a portion having a low density to cope with a head variation and other colors are used for a portion having a high density to make the banding or variation unnoticeable.
As for a solid image, JP-A-2003-63043 discloses a method that increases ejection amounts of the nozzles adjacent to pixels near a non-ejected nozzle so as to generate a solid image in the entire nozzles.
When a deviation in printing position of the dot is in a direction orthogonal to a nozzle arrangement direction, that is, a printing direction (paper feed direction) due to a flying curve phenomenon, such a banding phenomenon is not problematic in a case where a monochrome image is formed with one color ink. However, in case of a color image where dots of several colors are combined, a density of that portion may become darker than other portions, and color irregularity may occur.
Accordingly, a method of preparing a color conversion table per nozzle column in a printing direction and performing color matching to remove the banding phenomenon caused by the deviation in printing position in a printing direction is taken into account. However, this method requires a color conversion table per an amount of the deviation in printing position of the nozzle, and should consider the deviation in the printing position by four causes when ink of four colors of CMYK are used for printing. Accordingly, a capacity of the color conversion table to be prepared may expand. In addition, a very large color conversion table is required when each color data of RGB and CMYK is held by 8-bit (256 gray-scale values) data. For this reason, a memory (a storage device) or a device of processing a high-performance information operation (CPU or the like) is required, thereby causing a considerable increase in manufacturing costs.